Double Helix, Double-Piss-You-Off !
The way that you start the game is not good at all. They should've set a tutorial but you suddenly start in the middle of action in a dull envnmnt.
Limited saving times (Even if you've set them to unlimited) is not a good idea in this game. I don't know why developers insist on this bothering idea.
Boring! Sometimes all you've to do is to walk on and on through boring paths and shoot down some stupid enemies. The most annoying thing about the game was a hell of bugs. Bugs in graphic, in gameplay , bugs while saving, bugs while loading, bugs while setting up options ... Another annoying thing is dealing with your own character. You can't sometimes even switch weapons.
As much as I liked weapons in SOF1 I hate them in SOF2, especially the big stupid OICW. I won't recommand it for Single Playing at all.